Colorimetric anion sensor based on receptor having indole- and thiourea-binding sites

Abstract

A new colorimetric sensor L containing nitro-substituted indole and bisthiocarbonohydrazone units for selective fluoride and acetate ions is designed and synthesized. The receptor L shows well-defined color change in the visible region of the spectrum with an absorption band at ∼515 nm and 506 nm, respectively, for the F⁻ and CH₃COO⁻ ions in an acetonitrile solution. Job's plots indicated the formation of 1 : 1 (L with CH₃COO⁻) and 1 : 2 (L with F⁻) complexes. The interaction of L with the F⁻ ion undergoes a deprotonation process and release of [HX₂]⁻, whereas with the CH₃COO⁻ ion, it forms a stable [LH₂^…X]⁻complex. The relative affinities of the anions with L are rationalized using computational studies.